This invention relates to an apparatus for grinding an edge shape and peripheral surface configuration upon ophthalmic lenses.
The art of preparing ophthalmic lenses from glass blanks entails two major processes. First, the circular lens blanks are surface ground with a prescriptive front and back curvature to provide a desired optic quality or characteristic and thus enhance the vision of an ultimate wearer. Secondly, the lenses are ground to a desired edge shape to fit a preselected frame. Additionally, the peripheral edge surface of the lens is typically beveled or finished to cooperate with a reciprocal bevel on an interior peripheral surface of a frame in order to hold the lenses within the frame.
In the past at least one process of lens edging has been achieved by mounting a single lens upon a laterally fixed spindle or chucking mechanism and advancing an abrading wheel into lateral contact with the lens. The process is then repeated on an additional blank to produce a matching set or pair of lenses.
In another previously known process a lens to be edge ground is horizontally mounted about a vertical axis. A pair of grinding wheels are vertically mounted for rotation on either side of the lens for selective advancement into grinding engagement with the central lens. Each of the grinding wheels is fashioned with an oppositely sloping peripheral surface. Accordingly, one wheel contacts a front peripheral portion of the lens and another wheel contacts a back peripheral portion of the lens. In combination the two grinding wheels form a beveled peripheral edge on the lens. Lateral control of the abrading wheels is achieved by a pair of conical cam followers which ride against a generally disc shaped cam. Once completed, the lens is removed and the process is repeated on a second lens blank to produce a pair.
Although lens edging equipment of the foregoing and similar designs have received at least a degree of attention and acceptance in the art several significant difficulties exist. In this connection, edge grinding a pair of lenses on presently known machines is somewhat time consuming and requires a degree of operator attention and control.
Additionally, these previously known edging devices are limited to grinding a single lens at one time and thus lack a certain degree of uniformity and symmetry desired of a pair of lenses.
Further, the foregoing known machines do not provide a capability of edging a pair of lenses in a manner to sequentially remove glass and then fine grinding a desired edge configuration.
Still further, the known prior art devices do not exhibit a capability for simultaneously grinding a pair of lenses and facilely and independently varying the lens size for a given lens shape.
A significant advance was achieved in the art with the conception and reduction to practice of a dual headed edger such as disclosed in an application entitled METHOD AND APPARATUS FOR EDGING OPHTHALMIC LENSES by Messrs. Boyd Neisler and Joseph Stith commonly assigned with the subject application and filed on Jan. 24, 1978 as U.S. Ser. No. 871,871.
Although a complete description of the above invention may be had by referring to said patent, in brief sum, this invention entails an abrading wheel and first and second floating heads for rotatably supporting a pair of ophthalmic lenses on either side of the abrading wheel. The lenses are biased toward the wheel and are incrementally rotated about mutually parallel axes which lie parallel with a central longitudinal axis of the abrading wheel. A cam control system is operably connected to the lenses and serves to control incremental rotation of each of the lenses as well as lateral engagement of the lenses with the central abrading wheel. The Neisler et al. method includes the steps of mounting a pair of ophthalmic lenses upon axes parallel with a central axis of an abrading wheel, biasing the lenses toward the abrading wheel and controlling rotation of the lenses to be edge ground with a cam control system to produce a desired lens peripheral shape and edge surface.
Although introduction of the Neisler et al. system represented a singular advance in the art, room for further improvement remains. In this connection, the wide variety of glasses frames today requires a lens finisher to stock literally thousands of different mechanical cams (or patterns). It is estimated that an operator may use from time-to-time approximately 8,000 to 10,000 different patterns. This large variety of shapes requires a library file which is difficult and time consuming to maintain. Moreover, a complete library of accurately dimensioned patterns represents a significant initial capital investment.
The difficulties suggested in the proceeding are not intended to be exhaustive, but rather are among many which may tend to reduce the effectiveness and user satisfaction of prior lens edging methods and apparatus. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that ophthalmic lens edging machines and techniques appearing in the past will admit to worthwhile improvement.